# All files / services TranslationService.js

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     /**
     * Translation Service
     * Centralized translation management with i18n support
     */

    const fs = require('fs');
    const path = require('path');
    const { pool } = require('../config/database');

    class TranslationService {
      constructor() {
        this.translations = {};
        this.defaultLanguage = 'en';
        this.loadTranslations();
        this.refreshDefaultLanguage();
      }

      /**
       * Load all translation files
       */
      loadTranslations() {
        const localesPath = path.join(__dirname, '../locales');

        try {
          const files = fs.readdirSync(localesPath);

          files.forEach(file => {
            if (file.endsWith('.json')) {
              const lang = file.replace('.json', '');
              const filePath = path.join(localesPath, file);
              this.translations[lang] = JSON.parse(fs.readFileSync(filePath, 'utf8'));
            }
          });
        } catch (error) {
          console.error('Error loading translations:', error.message);
        }
      }

      async refreshDefaultLanguage() {
        try {
          const [rows] = await pool.execute(
            `SELECT setting_value FROM system_settings_kv WHERE setting_key = 'default_language' LIMIT 1`
          );
          if (rows && rows[0] && rows[0].setting_value) {
            this.defaultLanguage = rows[0].setting_value;
          }
        } catch (error) {
          console.error('Error loading default language:', error.message);
        }
      }

      setDefaultLanguage(language) {
        if (language && typeof language === 'string') {
          this.defaultLanguage = language;
        }
      }

      /**
       * Get translation for a key
       * @param {string} key - Translation key (e.g., 'errors.not_found')
       * @param {string} lang - Language code (default: 'en')
       * @param {object} params - Parameters for interpolation
       * @returns {string} Translated text
       */
      t(key, lang = 'en', params = {}) {
        const keys = key.split('.');
        let translation = this.translations[lang] || this.translations[this.defaultLanguage];

        for (const k of keys) {
          if (translation && translation[k]) {
            translation = translation[k];
          } else {
            // Fallback to default language
            translation = this.translations[this.defaultLanguage];
            for (const k2 of keys) {
              if (translation && translation[k2]) {
                translation = translation[k2];
              } else {
                return key; // Return key if translation not found
              }
            }
            break;
          }
        }

        // Interpolate parameters
        if (typeof translation === 'string' && params) {
          Object.keys(params).forEach(param => {
            translation = translation.replace(new RegExp(`{{${param}}}`, 'g'), params[param]);
          });
        }

        return translation;
      }

      /**
       * Get user's preferred language from request
       * @param {object} req - Express request object
       * @returns {string} Language code
       */
      getLanguage(req) {
        // Priority: 1. User preference, 2. Accept-Language header, 3. Default
        if (req.user && req.user.preferred_language) {
          return req.user.preferred_language;
        }

        if (req.headers['accept-language']) {
          const lang = req.headers['accept-language'].split(',')[0].split('-')[0];
          if (this.translations[lang]) {
            return lang;
          }
        }

        return this.defaultLanguage;
      }

      /**
       * Middleware to add translation function to request
       */
      middleware() {
        return (req, res, next) => {
          const lang = this.getLanguage(req);
          req.t = (key, params) => this.t(key, lang, params);
          req.lang = lang;
          next();
        };
      }
    }

    // Export singleton instance
    module.exports = new TranslationService();